Curie Point Writting CPW

7 On RBW scheme, was obtained that to magnetize a nano-dot, at approximately 14 kOe to 15 kOe of reversal field was required. This writing field, which in 10 4 Oe order, becomes inapplicable for magnetic recording application. On second part of this paper, reversal magnetic scheme on Curie Point Writing CPW that has aim to decrease amount of reversal field will be discussed. Fig. 8 shows a scheme of CPW. Supplying of heat randomize the initial magnetization of nano-dot, then nano-dot is made cooled abruptly until it reaches room temperature during 2.5 ns with influence of H to +x axis direction. H is supplied with a purpose to aligning the orientation of ferromagnetic nano-dot magnetization. The calculation is performed with variation of 50 randomized numbers. The probability of that cooling process called as reversal probability P that can be formulated by : n P N    where n is magnetization that parallel to H, then N is 50 th given random magnetization number. Minimum field is required to magnetized 50 th given random number parallel to H called as Threshold Field H T Figure 9. Dependence of P with respect to H on reversal magnetization with CPW scheme for a K ⊥ = 3.51  10 6 ergcm 3 , b K ⊥ = 3.51  10 6 ergcm 3 with coresponding value of 4 M s = 5697.5 G. From Fig. 9, can be observed the dependence of P with respect to bias magnetic field H. When H = 0, P = 0, it indicates that instant cooling does not magnetizes nano-dot spontaneously 8 parallel to +x axis. Therefore it needs H to magnetizes the nano-dot. However, if H is less than 600 Oe, it still has not been able to magnetizes nano-dot into +x direction. When the value of H is more than 600 Oe, P quickly increases until reach equal to 1. It means that 50 th given random number have the magnetization inline to H. Fig. 10 shows the declining of H T along with increasing of α for two different values of K ⊥ with equal 4 M s . Nano-dot with larger value of α has a tendency to be more easily directed to its bias magnetic field orientation. On the contrary, for smaller α, nano-dot get harder to directed to the bias field. It is caused by an amount of Gilbert damping that rotates more easily directed towards the bias field, therefore, smaller reversal field is needed to magnetizes the nano-dot. From presented value of H T in Fig. 10, it can be seen that there is a decreasing of reversal field value compared with result from the scheme of RBW that located in Fig. 5b. On the scheme of RBW, the magnitude of reversal field for two different value of K ⊥ with four variation of α is approximately at 14 kOe - 15 kOe. Meanwhile on CPW scheme, size of reversal field descend up to approximately at 1.4 kOe - 1.6 kOe. Therefore, from this result can be concluded that thermal activation can effectively decrease the magnitude of reversal field up to  90. Figure 10. Comparison of α with H T for two values of K ⊥ with 4 M s = 5697.5 G

4. CONCLUSSION

Micromagnetic simulation of perpendicular magnetized nano-dot has been performed to investigate the influence of Gilbert damping effect on thermally assisted magnetization reversal by solving Landau - Liftshitz Gilbert equation. At room temperature, for two different values of K ⊥ , have been obtained that decreasing of E along with the increasing of α is not followed by decreasing of H swt which tend to fluctuate. In addition, for nano-dot with larger K ⊥ , larger H swt is required which is followed by excalation of t swt . Activation of thermal has been succeeded to lowering an amount of reversal field up to  90. Moreover, H T could be reduced by Gilbert dam- ping increment. 9 5. REFERENCES [1] Wood R., Hsu Y a d “ hultz M. . Pe pe di ula Mag eti Re o di g Te h olog , i Hitachi Global Storage Technologies, White Paper, USA. [2] Jud , J. H. Past, P ese t a d Futu e of Pe pe di ula Mag eti Re o di g . Jou al of Magnetism and Magnetic Materials 235 2001 235 –240. [3] Wang, Y. 2011. Ph si s a d Mi o ag etik A al sis of Ad a ed Re o di g Te h ologies . Desertasi Doctor of Phylosophy Department of Electrical and Computer Engineering. Pennsylvania: Carnegie Mellon University Pittsburgh. [4] Pu a a B., Koga M., Nozaki Y a d Matsu a a K. . “to hasti “i ulatio of The all Assisted Magnetization Reversal in Sub- Dots ith Pe pe di ula A isot op . Department of Electronics .Kyushu University. Journal of Magnetism and Magnetic Materials 321 1325-1330 [5] Yoo “ a d K ish a K. M. . Te pe atu e Depe de e of Mag eti A isot op Co sta t i Ma ga ese Fe ite Na opa ti les at Lo Te pe atu e . J. appl. Ph s. , 07B534. [6] Mardona, Yasir M., Supriyanto E and Djuhana D.. . O se asi Pembalikan Magnetisasi Material Ferromagnet Bentuk Elemen Diamond- “haped De ga “i ulasi Mi o ag eti . U i e sitas I do esia . [7] Ma do a. . Di a ika Do ai Wall da Efek A isot opi pada Mate ial Fe o ag et Co da Ni Be e tuk Na o i e . Magiste Phisycs Thesis. Universitas Indonesia. [8] “ h efl T., Fidle J., “uess D., “ holz W., a d Tsia tos V. . Ha d ook of Mag eti Mate ials: Mi o ag eti “i ulatio of D a i a d The al Effe ts . Tsihua U i e sit Press. [9] L’u o i Ba as, . Nu e i al Methods for the Landau-Liftshitz-Gil e t E uatio , I Numerical Analysis and Its Applications, pp.158-165. [10] Nakata i Y., Uesaka Y a d Ha ashi N. Di e t “olutio of the La dau-Lifshitz Gilbert Equation fo Mi o ag eti s . Japa ese Jou al of Applied Ph si s, 28, pp. 2485-2507. [11] Nosaki Y., Iso aki Y., Hashi oto A., Pu a a B a d Matsu a a K. . Nu e i al A al sis of Thermally Assisted Magnetization Reversal in Rectangular MRAM Cell Consisted of E ha ge Coupled Bila e , Jou al Mag eti “o . , pp. -577. [12] Pu a a B. . The all Assisted Mag etizatio Re e sal i Pe pe di ula l Mag etized Thi Fil . Do to Thesis, Ele t o i s Depa t e t G aduated “ hool of I fo atio “ ie e and Electrical Engineering, Kyushu University : Japan.